Steady state vs Transcient surface integrals

ViLaks · October 30, 2017, 05:13

Hello All,

I am running a case of natural convection inside a domain wherein walls are maintained at -20 deg C and air cools down from 43 deg C to -18 deg C. I run this case both steady state and transcient. I plot The following surface monitor:
Integral ---> Wall Fluxes ---> Total Surface heat flux over the walls.
I run the transcient simulation until convergence (that is air cools down until -20 deg C). Now at the end of the simulation, the value of surface monitor in both the situations should be same right? If not what is the difference between the steady state and transient surface monitors?

Thanks
Vignesh

LuckyTran · October 30, 2017, 10:33

There is no difference, the surface monitor does not know what time it is. The surface monitor simply does the calculation based on the current solution (whether this is iteration or time) and outputs it.

If you get a difference result, then it seems your transient simulation converged to a different state than your steady state simulation. It is not the monitor's fault. Something happened differently in the solution.

Btw are you running natural convection inside a closed box? You must do this in transient. The steady solver is not meaningful because of issues enforcing continuity.

ViLaks · October 30, 2017, 23:10

Quote:

Originally Posted by LuckyTran

There is no difference, the surface monitor does not know what time it is. The surface monitor simply does the calculation based on the current solution (whether this is iteration or time) and outputs it.

If you get a difference result, then it seems your transient simulation converged to a different state than your steady state simulation. It is not the monitor's fault. Something happened differently in the solution.

Btw are you running natural convection inside a closed box? You must do this in transient. The steady solver is not meaningful because of issues enforcing continuity.

Dear Lucky Tran,

Thanks for your reply. Ya I know it is necessary to run transcient. I just wanted to check something. Actually the link to my problem is here, which is where I need inputs:

Temperature Pull Down Simulation using Fluent

By the way, my steady state and transient surface monitors return the same value

With Regards
Vignesh

LuckyTran · October 30, 2017, 23:40

That's fine. At least you know, or I hope you are convinced, it's not a problem with the surface monitors.

October 30, 2017, 05:13	Steady state vs Transcient surface integrals	#1
ViLaks Member Vignesh Lakshmanan Join Date: Nov 2016 Posts: 79 Rep Power: 9	Hello All, I am running a case of natural convection inside a domain wherein walls are maintained at -20 deg C and air cools down from 43 deg C to -18 deg C. I run this case both steady state and transcient. I plot The following surface monitor: Integral ---> Wall Fluxes ---> Total Surface heat flux over the walls. I run the transcient simulation until convergence (that is air cools down until -20 deg C). Now at the end of the simulation, the value of surface monitor in both the situations should be same right? If not what is the difference between the steady state and transient surface monitors? Thanks Vignesh

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October 30, 2017, 10:33		#2
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,677 Rep Power: 66	There is no difference, the surface monitor does not know what time it is. The surface monitor simply does the calculation based on the current solution (whether this is iteration or time) and outputs it. If you get a difference result, then it seems your transient simulation converged to a different state than your steady state simulation. It is not the monitor's fault. Something happened differently in the solution. Btw are you running natural convection inside a closed box? You must do this in transient. The steady solver is not meaningful because of issues enforcing continuity.

October 30, 2017, 23:40		#4
LuckyTran Senior Member Lucky Join Date: Apr 2011 Location: Orlando, FL USA Posts: 5,677 Rep Power: 66	That's fine. At least you know, or I hope you are convinced, it's not a problem with the surface monitors.